General synonyms:
* Prisoner: Implies someone held against their will, usually in a physical prison.
* Hostage: Someone held against their will, often for a ransom or political purpose.
* Detainee: Someone held by authorities, often for questioning or investigation.
* Confined: Restricted in movement or freedom.
* Imprisoned: Held in a prison or other place of confinement.
* Bound: Tied or restrained, possibly both physically and emotionally.
* Enslaved: Forced to work against their will.
More specific synonyms:
* Captive audience: A group forced to listen or watch, as in a theater or lecture.
* Taken hostage: Seized and held for a specific purpose.
* Incarcerated: Officially confined in a prison.
* Held in custody: Officially detained by authorities.
* Subjugated: Brought under control and forced to submit.
The best synonym to use will depend on the specific situation and the desired level of formality.